"The aim of philosophy," the great American philosopher Wilfrid Sellars once wrote, "is to understand how things in the broadest possible sense of the term hang together in the broadest possible sense of the term." In other words, the goal of philosophy is to produce a (comprehensive) list of all entities conjoined with a (correct) description of their interrelations. We may call the global system comprised of all entities and all their interrelations "the structure" of the world. In those terms, the aim of philosophy is to understand the structure of the world.
In investigating the structure of the world, the first question that arises is whether the world has a structure independently of how we perceive and conceive it. In everyday life, we instinctually assume that what entities there are, and how they are interrelated, are by and large independent of us and our way of thinking of the world. But philosophers have long suspected that the truth may be subtler than that. The first methodical philosophers in ancient Greece already spoke of the logos of reality - that which makes it intelligible. More modern philosophers have sometimes made the dependence of the structure of the world on intelligent perceivers more explicit. The eighteenth-century German philosopher Immanuel Kant's view was particularly compelling: the world may have an absolute and mind-independent structure, but if so we can know nothing of it; the only thing we can understand is the structure the world has relative to our thought and perception.
Perceiving things, conceiving of them, thinking about them - these are different ways of representing things. Thus from a Kantian perspective, the only intelligible structure of the world is the structure it inherits from the way we represent it. To that extent, understanding the structure of the world requires prior understanding of the structure of representation. Thus within a Kantian framework, the nature of representation - how the mind carves up the world - quickly becomes a central philosophical enterprise.
This is not the only way the notion of representation can become philosophically central, but it is how I was led to focus on it in The Sources of Intentionality. The term 'intentionality' is somewhat infelicitous, in that it suggests a connection to intention and the will. In philosophical circles, the term is used differently, in a manner derived from the Latin term 'intentio,' which means something like 'directedness.' Focusing on this notion, certain medieval philosophers considered that the essence of representation is to direct itself onto something other than itself. When we perceive a butterfly landing on a tulip, our perception is directed onto the butterfly and the tulip; when we think of El Greco's Godward-stretched figures, our thought is directed at those peculiar figures; and so on. To inquire after the sources of intentionality, in that technical sense of the term, is to ask for the basis of our capacity to direct our perception and thought onto the world. The question is: What is it about our mind that bestows on it the capacity to direct itself outward?
Sadly, in The Sources of Intentionality I offer not one but two possible answers to this question. I say 'sadly' because I wish I was certain enough of my philosophical conclusions to home in on a single maximally plausible answer. In reality, my research has led me to vacillate between two coherent, stable, and internally compelling accounts of the source of mind's directedness, each carrying its own distinctive attractions as well as its own characteristic liabilities.
The first account proposes that directedness is a primitive power of consciousness - human and animal consciousness alike. There is something about our conscious experience that endogenously directs it onto the world, a feature we cannot explain in terms of anything more basic. We can shed light on this primitive power of consciousness by investigating its subjective feel from a first-person point of view, but no objective, third-person, reductive explanation of it is possible. The main attraction of this account is that it makes sense of our ability to hallucinate and imagine all manners of curious events and objects that have no grounding in anything outside the sovereign borders of inner consciousness. The main liability of the account, however, is its anti-scientific and borderline mysterious air: it is unclear how to integrate this kind of primitive power of consciousness into a mature scientific conception of the world.
The book's second proposed account of the sources of intentionality is much more scientifically respectable. It grounds the mind's capacity for directedness in neural coalitions in the (human as well as animal) brain, neural coalitions very much susceptible to scientific inquiry. In particular, it suggests that certain neural coalitions are responsive to patterns in the external environment, and can occur only when those patterns are present. As a result, these coalitions can be said to track the presence of those patterns. Furthermore, some of our brain's neural coalitions are so sophisticated that they track not only environmental patterns, but also the very tracking of those patterns. The brain is a sort of complex two-story machine: on the ground floor, it is busy monitoring the environment outside the skull; on the second floor, it is busy monitoring the activity of the first floor. This design, allowing for both environmental tracking and "tracking of tracking," enables the brain to track the external environment in a self-aware manner. According to the book's second account, this design-based ability for self-conscious tracking is the source of the mind's capacity for directedness. As alluded to above, the great attraction of this account is its amenability to a thoroughly scientific understanding of representation. Its main liability, however, is its limited resources in making sense of the aforementioned sovereignty of the mind, its occasional tendency to hallucinate or imagine matters entirely unconnected to anything in the external environment.
The book endorses neither of the two accounts very assertively, but note that both ground directedness in aspects of conscious experience: either a primitive power of consciousness, or a self-conscious capacity for tracking the environment (itself grounded in a capacity for tracking-of-tracking). To that extent, the book recommends understanding the structure of representation through understanding the structure of consciousness. From this perspective, the Kantian approach to revealing the ultimate structure of the world becomes a four-stage endeavor. Stage 1: consciousness. Stage 2: from consciousness to representation. Stage 3: from representation to reality. Stage 4: reality. Together, these should lead to a philosophical system, of recognizably Kantian bent, that grounds the structure of the world in the structure of consciousness. The Sources of Intentionality effectively attends to Stage 2 of this enterprise. My previous book, Subjective Consciousness, addressed Stage 1. A book currently in the planning turns its attention to Stage 3.